The present invention relates to cylinder locks and, in particular, it concerns cylinder locks which employ pins which are rotatable.
Cylinder locks can be broadly subdivided into conventional or "Yale-type" locks in which the key has a jagged edge and flat-key locks in which a generally flat key features various patterns of depressions. In both cases, the various features of the key serve to displace a number of pins, generally in a direction perpendicular to the direction of insertion of the key, to predefined positions which allow rotation of the cylinder.
In order to increase the number of "combinations", and hence the security, of a lock, various Yale-type locks have been designed to allow rotation as well as displacement of the pins. In this case, the pins typically have a chisel-like end for engaging slightly angled recesses in the jagged pin-engaging edge. Examples of such designs may be found in U.S. Pat. Nos. 3,499,303 to Spain, 3,722,240 to Spain et al., 4,098,103 to Raskevicius, 4,328,690, 4,635,455 and Re. 31,910 to Oliver, Re. 30,198 to Oliver et al., 4,741,188 to Smith, 4,932,229 to Genakis and 5,067,335 to Widen.
Clearly, the range of angles which can be effectively defined by the shape of a recess in the jagged edge of a narrow key are extremely limited, typically lying within a range of at most .+-.20.degree. from the perpendicular to the insertion direction. To avoid the possibility that the chisel-like ends of the pins could sit at an angle from which the shape of the key might not return them to the required angular position, rotation of the pins is limited to corresponding range of angles. This is typically achieved by a retaining element engaged in a slot around part of the periphery of each pin.
In the context of flat-key cylinder locks, PCT Publication No. WO 96/27724 discloses a number of configurations which employ rotatable pins. The main features of these configurations will now be described with reference to FIGS. 1-6. Specifically, FIGS. 1 and 2 show the disclosed form of flat key 10 which is formed with a number of pin-engaging seats 12. As seen in the enlarged view of FIG. 2, each seat 12 is formed as a fairly short slot extending at a given angle to the direction of insertion. The slots have an approximately V-shaped cross-section with rounded ends. The corresponding cylinder structure is shown in FIG. 3 while FIG. 4 shows an individual pin 14 therefrom. Pin 14 has a chisel-shaped end 16 similar to that described above in the context of Yale-type locks.
Unlike Yale-type locks, the direction of extension of the slots in a flat key are not inherently limited to a small range. Thus, key 10 may feature seats 12 with slots at angles ranging from approximately parallel to the extensional direction to approximately perpendicular thereto. At the same time, it should be noted that any given direction of slot is only effective to rotate a pin to the corresponding angle if the pin starts within a relatively small range of angles therefrom. The reasons for this will be apparent from FIGS. 5A-5C.
Specifically, referring to the enlargement of a shallow seat 12a in FIG. 5B, it will be seen that, over a large range of angles corresponding to as much as 120.degree., the crest of the chisel-shaped end 16 of pin 14 (represented by dashed lines) catches on the flat part of the key surface surrounding the slot such that the slot is ineffective to turn the pin. Even for a deeper seat 12b as shown in FIG. 5C, the pin-slot geometry may be ineffective to turn the pin to the correct position from initial positions over a range of as much as 90.degree.. Since the pin is restricted to rotation about its axis, the end of the pin only experiences a component of the inclination of the slot walls parallel to a tangent taken at the point of contact about the pin's axis. Since the local inclination of the walls of the slot is directed perpendicular to the length of the slot, any significant initial misalignment between the pin and the slot greatly reduces the effect of the slot inclination for turning the pin. As a result, the proposed cylinder structure illustrated in FIG. 3 provides a projecting ridge 18 on each pin 12 which engages a peripheral slot 20 around part of the pin channel to delimit rotation of each pin to a range of no more than about 60-80.degree. including the required position.
The restriction of pins to a specific range of angular positions has a number of disadvantages. Firstly, the additional features required on both the pins and within the cylindrical plug add considerably to the cost of manufacture. Additionally, the restricted angular positions greatly limit the number of different combinations which can be achieved with a given number of pins, thereby reducing the level of security unnecessarily. The restricted angular movement also facilitates picking of the lock, particularly for pin angles adjacent to the ends of the available movement.
Parenthetically, reference is here made to FIGS. 6A-6D which illustrate an alternative implementation of the aforementioned PCT Publication No. WO 96/27724 in which the V-shaped slot is implemented on the end of pin 14 (FIG. 6B) while the chisel-shaped ridge is implemented as a ridged insert 22 (FIG. 6A) for insertion into a recess of key 10 as shown in FIG. 6C. Insert 22 may be formed with a transverse slot as shown to allow a user to set its angle by use of a screwdriver tool. Here too, the proper operation of the slot-ridge geometry is limited to a narrow range of angles, as indicated in FIG. 6D.
Referring again to FIG. 3, it will be noted that the lock of PCT Publication No. WO 96/27724 employs a sidebar 24 which engages a slot running along the inside of the cylinder housing to prevent rotation of the cylinder plug until all pins are aligned. This structure, predominant also in the Yale-type rotating pins locks mentioned above, exhibits weakness against forces exerted parallel to the cylinder axis. Where conventional driver pins aligned with the pins are used in addition to the sidebar, this problem is not critical. In the absence of driver pins, however, such locks are prone to attack using a pulling extractor tool.
Turning finally to FIGS. 7 and 8, there is shown a further feature disclosed in PCT Publication No. WO 96/27724 in which a pin is raised to a position lying outside the keyway of the cylinder. This is achieved by providing the key with a "floating pin" 26 which is effectively a movable insert mounted in a hole formed through the key so as to be displaceable so as to project above the surface of the key. The cylinder is fitted with a spring-biased actuator 28 opposite the pin in question so that, when the key is inserted, actuator 28 displaces floating pin 26 so as to make pin 14 retract along its channel to a position lying outside the keyway.
While the floating pin assembly makes unauthorized copying of keys difficult, it does so at great cost. Firstly, the assembly requires significant modification of the cylinder to provide the actuator 28, thereby adding to production costs. Additionally, the assembly may facilitate picking of the lock since actuator 28 readily identifies both the presence and position of a pin which must be displaced to a position lying outside the keyway.
There is therefore a need for a flat-key cylinder lock which would allow the use of pins which can turn unrestricted through 360.degree., and effective pin and key geometries for use in such a lock. It would also be highly advantageous to provide a flat-key cylinder lock with rotatable pins which would avoid the use of a sidebar. Finally, it would be highly advantageous to provide a flat-key structure which would raise a pin to a position lying outside the keyway without requiring significant modification of the cylinder structure.